Mann-Whitney U Sample Size Calculator
The Mann-Whitney U test is a popular non-parametric test used to compare two independent samples. The sample size calculator for this test helps you determine the minimum sample size required to achieve a desired level of statistical power.
- Select the significance level (α).
- Enter the desired power (1 – β).
- Enter the effect size (d).
- Click ‘Calculate’.
The formula used in this calculator is based on the work of Cohen (1988) and is as follows:
| Effect Size (d) | Sample Size (n) |
|---|---|
| 0.5 | 64 |
| 0.8 | 25 |
| 1.2 | 13 |
- Always ensure your data meets the assumptions of the Mann-Whitney U test.
- Consider using a power analysis to determine the appropriate sample size before starting your study.
- Remember that increasing the sample size increases the power of the test.
What is the difference between significance level (α) and power (1 – β)?
The significance level (α) is the probability of rejecting the null hypothesis when it is true. Power (1 – β) is the probability of rejecting the null hypothesis when it is false.